1. Field of the Invention
The invention comprises a traction motor with a single stator and two rotors for use in a hybrid vehicle powertrain to complement power delivered to traction wheels by an internal combustion engine.
2. Background Art
Hybrid electric vehicle powertrains have been developed for contemporary automotive vehicles to improve hydrocarbon fuel efficiency and to reduce undesirable exhaust gas emissions. An electrical induction motor and battery subsystem is especially adaptable for such hybrid electric vehicle powertrains because of the robustness and compact size of an induction motor. Further, an induction motor has reasonably high efficiency and design simplicity. It can be controlled using known control technology so that the most efficient operating range of the motor and the most efficient operating range of the engine are used during vehicle traction torque delivery. Further, regenerative braking is available.
It is possible in powertrains of this type to use multiple motor drives, which require two power inverters together with a common motor controller. The use of multiple motors, however, increases the manufacturing cost and creates packaging problems in an automotive vehicle powertrain. The requirement for a separate power inverter for each motor also causes undesirable complexities in the overall powertrain design.
U.S. Pat. No. 6,585,066 discloses a multiple ratio power transmission mechanism for use in a hybrid electric vehicle wherein an induction motor is located in a torque flow path between an internal combustion engine and a multiple ratio transmission. The motor and the engine define parallel power flow paths to the torque input side of the transmission. The transmission includes planetary gearing with clutch and brake mechanisms for establishing plural torque flow paths through the transmission to the vehicle traction wheels. An engine clutch is used to disconnect the engine from the powertrain when the vehicle stops or coasts. When the vehicle operates under low power driving conditions, the power flow path from the motor may be used exclusively. Energy may be recovered during coasting when the vehicle operates in a coast braking mode. Under heavy throttle acceleration conditions, the added torque available from the motor augments torque developed by the internal combustion engine.
In a powertrain of the kind disclosed in U.S. Pat. No. 6,585,066, the motor can be used to drive the vehicle if the engine clutch is off. When the engine clutch is on, the motor and the engine can both drive the vehicle as torque flow paths are developed by the transmission gearing. When the electric motor is driving the vehicle and the power demand requires the engine to be started, the motor must not only maintain the required torque level at the wheels, but it must also overcome the torque required to compress the engine fuel-air charge in the engine cylinders as well as the friction of the engine. This added torque demand on the motor, which is temporary during the engine starting cycle, may cause a sharp reduction in driveline torque. This can cause undesirable torsional oscillations in the driveline.